An Etymological Dictionary of the German Language/Eiche
Eiche, f., ‘oak, oak-tree,’ from the equiv. MidHG. eich, OHG. eih (hh), f.; a term common to Teut., but by chance not recorded in Goth. (*aiks, f.); comp. Du. eek (eik), AS. âc, f., E. oak. In Iceland, where there are no trees, the old word eik, f., received the general meaning ‘tree’ (for a similar change of meaning see Esche, Föhre, Tanne; comp. Gr. δρῦς, ‘oak, tree (generally).’ The term aik- is peculiar to Teut.; whether it is connected with OIc. eikenn, adj. ‘wild,’ and with the Sans. root êj, ‘to shake,’ is undecided.